Plasmonic nanostructures can be used to tackle the shortcomings of conventional photosensitizers in photodynamic therapy (PDT) of cancers, including their low reactive oxygen species (ROS) quantum yield, stability, and targetability. However, the positive role of plasmonic nanostructures is not limited to their ability for ROS generation or singlet oxygen formation. The main advantage of plasmonic nanostructures relies on the collective oscillation of free electrons, the so-called surface plasmon resonance (SPR), which can trigger plenty of optical phenomena in their near-field. Surface plasmon resonance is highly dependent on the morphology, size, and composition of the plasmonic nanostructure, which can give one the ability to control the wavelength of light-matter interaction, which is highly desirable in PDT applications. This review has focused on the conjugation of plasmonic nanostructures with organic compounds, biological compounds, ceramic nanoparticles, polymeric nanoparticles, metal-organic frameworks (MOFs), and magnetic nanoparticles from a mechanistic point of view. Hybridization of plasmonic nanoparticles would enable plenty of optical mechanisms beneficial for the PDT process that has been extensively discussed by presenting the most recent efforts in each category. This review can be a useful guideline for researchers working on enhancing the efficiency of the PDT process and those interested in plasmon-enhanced phenomena by emphasizing the underlying mechanisms.